Color morph, habitat and diet influence the territory size and shape of Zonotrichia alibicollis (White-throated Sparrow)

Abstract

The ideal free distribution (IFD) and ideal despotic distribution (IDD) theories predict how animals distribute themselves among habitats relative to resource quality and quantity. They differ in expectations of whether individuals are competitively equal and free to move between habitats (IFD), or if dominant individuals occupy higher quality habitats subjugating subordinates into poorer habitats (IDD). However, the phenotype-limited IFD is offered as an alternative theory for when phenotype-specific behaviors interact with resource quality to influence space use dynamics. Zonotrichia albicollis (White-throated Sparrow) is polymorphic and white colored morphs are more aggressive than tan morphs with previous research indicating no morph-specific differences in territory characteristics suggesting conformity to the IFD. We fitted archival GPS tags to 68 white and tan morph Z. albicollis in grids adjacent to wetlands (shoreline forest) and >600 m from wetlands (interior forest) in the boreal forest of Saskatchewan, Canada, to measure territory size and shape in response to morph, body size, habitat, conspecific density, invertebrate biomass, diet, and diet quality (plasma fatty acids). Territory size, notably for white morphs, was smaller in shoreline compared to interior forests and was predicted by the proportion of dietary aquatic emergent insects and conspecific density. White morph territories were also more irregularly shaped in shoreline forests compared to tan morphs. White morph territories were also more irregularly shaped in shoreline forests compared to tan morphs due to diet. Birds occupying shoreline habitats had higher eicosaptaenoic acid and lower omega 6: omega 3 fatty acids. Overall, shoreline habitats appeared to provide higher quality resources as evidenced by higher quality diets, greater conspecific density and overall territory sizes being smaller and more irregularly shaped at least for white morph birds. Our results suggest Z. albicollis align with the phenotype-limited IFD resulting from a complex interplay of habitat type, conspecific density, diet and behaviour influencing territory characteristics.